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Characterization and Potential of Dual Fuel 2011-01-2223

Published
Combustion in a Modern Diesel Engine 09/13/2011

Fredrik Königsson and Per Stalhammar

AVL Sweden

Hans-Erik Angstrom
Royal Institute of Technology

Copyright © 2011 SAE International

doi:10.4271/2011-01-2223

operation due to the higher H to C ratio of methane. Methane

ABSTRACT is also what is referred to when the term Biogas is used, only
Diesel Dual Fuel, DDF, is a concept which promises the this time the methane comes from a renewable source which
possibility to utilize CNG/biogas in a compression ignition means that an even greater reduction in greenhouse gases is
engine maintaining a high compression ratio, made possible possible.
by the high knock resistance of methane, and the resulting
benefits in thermal efficiency associated with Diesel The diesel engine is currently the dominating prime mover in
combustion. commercial applications, due to its highly desirable operating
characteristics such as high efficiency and reliability.
A series of tests has been carried out on a single cylinder lab Methane is currently used mainly in spark ignited engines,
engine, equipped with a modern common rail injection both in passenger cars and in heavy duty commercial
system supplying the diesel fuel and two gas injectors, placed vehicles. Diesel Dual Fuel, DDF, is a concept where a
in the intake runners. One feature of port injected Dual Fuel combination of methane and diesel is used in a compression
is that full diesel functionality is maintained, which is of great ignited engine, maintaining the high compression ratio of a
importance when bringing the dual fuel technology to market. diesel engine with the resulting benefits in thermal efficiency.
The objective of the study was to characterize and investigate Currently, work is carried out both in the field of direct
the potential for dual fuel combustion utilizing all degrees of injected DDF, where both methane and diesel is direct-
freedom available in a modern diesel engine. injected into the combustion chamber, as well as port injected
DDF where the methane is injected in the intake manifold
Increased diesel pilot proved efficient at reducing NOx and is premixed with the air during induction and
emissions at low λ. Advanced combustion phasing has the compression. The work presented in this paper focuses solely
potential to extend the lean limit for operation. Stoichiometric on the latter and henceforth this is what is referred to when
operation using high levels of EGR is identified as a the acronym DDF is used. Port injected DDF has the benefit
promising field in conjunction with raised inlet temperature. of making conversion of existing vehicles relatively simple
and maintaining full diesel capability in case methane is
unavailable. Both of these factors are important when
INTRODUCTION bringing the technology to market.
Methane is a clean burning fuel with a high resistance to
knock, which makes it suitable for use in internal combustion The main drawbacks of DDF include high emissions of
engines. It is the main component of CNG which is available unburned methane from crevices, partial misfire and flame
throughout the world at competitive prices. Although CNG is quenching in the lean mixture at low load and problems with
a fossil fuel, a 25 percent reduction in the emission knock and preignitions at high load. As increasingly stringent
greenhouse gases is obtained compared to diesel or gasoline emission legislation imposes the need for more careful λ-
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Table 1. Parameters investigated

control for diesel engines, the Euro VI engine platforms are A sweep in λ, from stoichiometric to the lean limit is carried
likely fitted with a throttle and a wastegate equipped out at each load point for different settings of some influential
turbocharger, features normally associated with the spark parameters. This identifies the key tools available for
ignited engine, SI-engine. The DDF engine is usually derived extending the lean limit or reaching stoichiometric
from a diesel engine. As these aforementioned features, the conditions, the desirability of which depends on the choice of
throttle and the wastegate, make their way into production aftertreatment and overall strategy chosen. The sweep in λ is
diesel engines, the degrees of freedom available for DDF performed by changing the inlet pressure and correcting the
operation increase as well without increasing the costs of amount of methane injected so that the desired BMEP is
conversion. maintained. Results will be presented for 13 and 6.5 bar
BMEP, and the parameters listed in Table 1.
OBJECTIVES
At the baseline setting the size of the diesel pilot results in a
The aim of this research is to investigate the potential for dual diesel substitution rate of approximately 98% on an energy
fuel combustion when λ-control is available and discuss basis. The additional settings, 29mg and 48 mg result in 80%
selected combustion phenomena that occur between and 70% diesel substitution respectively.
stoichiometric conditions and the engine lean limit. To
achieve good response and to control emissions during a load
transient in a lean burn engine, the DDF combustion process THEORY
must be thoroughly understood in this λ-range. The load The way that DDF is usually applied is that a homogenous
points displayed in Figure 1 have been studied in a single mixture of methane and air is inducted into the cylinder and
cylinder engine and a subset of these points is selected and compressed. Late during the compression stroke a small pilot
presented in this publication. The choice of operating points injection of diesel fuel is direct injected and serves as a liquid
is considered relevant based on data from long haulage spark plug, providing an ignition source for the methane.
vehicles in commercial traffic; the engine operates for most DDF heat release typically consists of three parts [2]:
part in a relatively narrow speed range around 1400 RPM.
1. Combustion of the diesel pilot
2. Combustion of methane in and in the immediate vicinity
of the diesel spray

3. Flame propagation through the methane-air mixture

Depending on load and a number of parameters, each of these

parts will contribute to a different degree to the accumulated
heat release. The term diesel substitution rate is used to
quantify the contribution from each fuel to the total amount
of energy supplied. It is further explained in Figure 2.

Figure 1. Load points selected for this publication

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the inherent costs and complications when employing EGR

[4], [6], [7].

PILOT SIZE
The influence of the size of the diesel pilot at high λ in a DDF
engine is well known; increasing the size reduces the
emissions of unburned HC but increases the NOx emissions
[5]. During much diluted operation with λ values typically
Figure 2. Diesel substitution, percent of the fuel, on an associated with diesel engines, the combustion of the diesel
energy basis, that is replaced by CNG pilot is the source of NOx formation since it takes place in a
heterogeneous environment with regions close to
The definition of Lambda in a DDF application is not self stoichiometric where high local temperatures exist [2]. The
evident. For this publication the following definition has been influence of pilot size at richer mixtures and low λ operation
used: is much less documented. In the baseline case a very small
pilot injection is used with associated high diesel substitution
since this is desirable for future DDF applications. Cooling of
the diesel injector tip is one reason to deviate from this
(1) strategy and increase the pilot at rich mixtures.

The parameters evaluated in this publication can be expected

to have the following effects on the performance of the
INLET TEMPERATURE
engine: In the DDF engine, the inlet temperature is both a challenge
and a tool. High inlet temperatures are a challenge in the
respect that they will increase the tendencies towards knock
COMBUSTION PHASING and preignitions, high temperatures increase NOx production
There are many reasons for deviating from maximum brake and heat losses and reduce the volumetric efficiency of the
torque (MBT) combustion phasing when calibrating an engine. At the same time it is a tool in improving the
engine. The most common reasons for employing late combustion quality of dilute mixtures, improving the
combustion phasing is to decrease engine out NOx, avoid tolerance for high EGR and reducing the emissions of HC
exceeding the limit for peak firing pressure or running into and CO [6].
knock or preignitions. Combustion phasing is also an
important tool for thermal management with regards to the
aftertreatment system. In addition to this, advanced
EXPERIMENTAL SETUP
combustion phasing can be expected to extend the lean limit ENGINE
of a lean burn DDF engine through higher temperatures
The measurements have been carried out on a single cylinder
during combustion [4], [6].
Scania lab engine available at the Royal Institute of
Technology in Stockholm, Sweden.
EGR
The use of exhaust gas recirculation, EGR, is a common The engine has a displacement of 2 l and is equipped with a
practice in diesel engines to control the NOx emissions high pressure common rail system, Scania XPI, as well as gas
through in cylinder measures and avoid excessive load on the injectors from Keihin, placed in the intake runners. The
NOx aftertreatment system or eliminate the need for such piston and piston crown are from Scania's current line of Euro
aftertreatment completely. EGR is also used in stoichiometric V engines.
and lean burn SI engines to reduce pumping losses and
thermal load. In the DDF engine, all of the above stated Auxiliary systems are in place for heating or cooling of intake
reasons to employ EGR apply. Since the DDF engine is air, oil, fuel and water. A supercharged SAAB engine is run
usually derived from a base diesel engine, the cooling system in an adjacent room, providing hydraulic pressure for the
and materials used in the cylinder head, exhaust manifold and brake and supplying the EGR when desired. When evaluating
turbocharger are not rated for the thermal loads associated the data, the stoichiometric EGR from the SAAB engine is
with stoichiometric operation. The use of EGR as an inert translated into the equivalent EGR ratio, had the EGR been
bulk gas to reach stoichiometric operation while maintaining generated at the current operating conditions.
acceptable incylinder and exhaust temperatures has great
potential to reduce the cost and complexity of the In addition, the engine is also fitted with a common rail gas
aftertreatment system by enabling the use of the three way injection system with two gas injectors, one in each intake
catalyst (TWC). This benefit will have to be weighed against runner. The rail-pressure for the methane was maintained at
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2.8 bars above intake pressure by an automatic pressure A rapid self tuning heat release script is implemented into the
regulator to simplify the prediction of injected mass based on controller, which calculates the heat release in real-time and
the ontime of the injectors. enables automatic cycle to cycle control of the combustion
phasing [3].
Table 2. Engine specifications

Figure 3. Schematic of the control system used

DATA ACQUISITION
CONTROL SYSTEM
Emissions of NOx, HC and CO and the EGR level was
Both data acquisition and communication with the test bed
measured using a Horiba EXSA-1500 exhaust analyzer.
were performed using an in-house software; CELL4, which
Smoke was measured with an AVL 415 smoke meter and an
runs on a PC and is supported by several PIC-processors.
AVL 4390 Opacimeter. For fuel metering, an AVL 733 fuel
balance was used for the liquid fuel and an Alicat Scientific
For direct control of the injection system, and indirect control
500 SLPM-type gas flow meter for the methane.
of the test bed through CELL4, AVL RAPTOR was used.
RAPTOR is an open source rapid prototyping system for
The pressure history was recorded at 0.1 CA increments,
engine control which is based on Simulink models and
using an AVL QC32D pressure transducer and a Kistler 5011
executed on dSPACE hardware [1]. The Simulink controller
charge amplifier.
is automatically translated into c-code which in turn is run in
real-time on the hardware. The control system can also be
simulated offline together with an engine/vehicle model. This RESULTS & DISCUSSION
enables the developer to easily test, calibrate and verify new Figure 4 shows a summary of the whole study with regards to
concepts and ideas before they are tried on an actual engine. the trade-off between BSHC and BSNOx, which are the most
challenging emissions to control in a DDF engine. The figure
The complete RAPTOR system consists of: includes results from the variation of other parameters, not
• ECM controller included in this publication. The most interesting results are
• Engine/Vehicle model located in the bottom left corner and they, along with the
results for the baseline setting, are labeled in the figure and
• dSPACE hardware selected for further discussion.
• Auxiliary tools e.g. to help analyze data and calibrate the
engine The effect of each parameter is discussed later in this report
in separate subsections. When interpreting the data it must be
Figure 3 shows a screenshot of the Simulink model when taken into account that the measurements are carried out on a
used for offline simulation. The same model is used both for single cylinder engine and parameters such as exhaust
simulation and for online control. The transition and variant backpressure and parasitic losses from the injection system
management are handled by GUI and scripts which provide and coolant pumps differ from what is encountered in a full
ease of use. For this project the drive stages built into engine. For this reason brake specific emissions results,
RAPTOR handled both the Keihin gas injectors as well as the BSHC and BSNOx are calculated with regards to indicated
Scania XPI diesel injector. torque as opposed to brake torque. IMEP for the high
pressure cycle; IMEPnet has been used as base for the
emission calculations.
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Figure 4. Trade-off between BSHC and BSNOx for a large set of operating points at 13 bar BMEP

COMBUSTION PHASING
The effects of combustion phasing is presented for 6.5 bar
BMEP. When throttling the intake air at loads of 6.5 bar
BMEP and below to reach richer mixtures; the limit is
eventually reached when the pressure and temperature at the
end of compression are too low to provide a reliable, stable
diesel ignition. At 6.5 bar BMEP, this meant that the rich
limit for DDF operation was approximately λ=1.2.

It is likely that this can be addressed by increasing the

temperature of the inlet air. This leads to lower λ since less
air is being inducted because of lower density and the
increased temperature also improves the diesel ignition. The
emissions results with regards to BSNOx and BSHC are
presented in Figure 5.

Figure 5. Emissions of HC and NOx versus λ for three

different combustion phasings at 6.5 bar BMEP
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Figure 6. Temperature and rate of heat release versus CA for three different combustion phasings at 6.5 bar BMEP, λ=1.8

It is shown in Figure 5 that the HC emissions are practically It is shown that the mean in-cylinder-temperature during
identical between λ=1.2 and λ=1.6, regardless of combustion combustion increases as the combustion phasing is advanced.
phasing. This indicates that the HC emissions are the result of Since the rate NOx formation is dependent on temperature in
crevice losses and that they are difficult to reduce further a non-linear way, a small increase in peak temperature will
without addressing the geometry of the piston and piston ring lead to a disproportionally large increase in NOx. When the
assembly. At mixtures leaner than λ=1.6, the emission results peak temperature increases from roughly 1700 K to ∼1950 K
start to deviate and it is clear that the early combustion the NOx emissions double. As the expansion progresses, the
phasing provides slightly better combustion quality than the mixture becomes cooler and below a certain temperature the
baseline case using MBT timing and much better than late oxidation stops. When the combustion is phased later there is
combustion phasing. The reason for this is the higher less time before this limit is reached, meaning less time for
temperature at which the combustion takes place. This is oxidation. This is the explanation for the increase in HC
illustrated in Figure 6 where temperature and rate of heat emissions when combustion phasing is retarded. There is also
release, ROHR, are displayed as a function of CA for λ=1.8. a difference in the ignition behavior of the methane; when the
combustion is retarded there is increased separation between
the peak corresponding to the premixed diesel combustion
and the main part of the heat release that corresponds to
flame propagation through the methane-air mixture. One
explanation for this is that the diesel is injected close to TDC,
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this leads to a shortened ignition delay which in turn much of the incitement for excessive boosting. The mean
decreases the time for mixing between the diesel and the charge temperature and ROHR for stoichiometric operation
methane. using 0, 20 and 40 % EGR is shown in Figure 8 40% EGR
has a severe effect on the combustion stability and HC
EGR emissions at lean mixtures but as a tool to reach
stoichiometric conditions it shows great promise. When going
The use of a diesel pilot as ignition source for the methane as
from 0% to 40 % EGR at λ=1, BSHC emissions increase
opposed to a spark plug has great benefits as far as EGR is
from 2.4 to 4.9 g/kWh and BSNOx decreases from 19.6 to 2.4
concerned. The ignition energy available is several orders of
magnitude greater when using a diesel spray; this vastly g/kWh. The reduction in NOx emissions is explained by the
increases the EGR tolerance, thus enabling stable operation large decrease in cylinder charge temperature.
of the engine at high EGR rates. At 40% EGR, the size of the
diesel pilot is increased slightly to improve combustion The ROHR for the baseline case shows a peak at
stability; the diesel substitution rate is still above 95%. As approximately 8°ATDC, this indicates a rapid combustion of
mentioned earlier, EGR can be utilized for many purposes in the end gas in the squish volume. This is likely due to bulk
a DDF engine, to reduce NOx, pumping losses and to enable ignition of the end gas, a phenomena previously discussed by
stoichiometric operation with acceptable thermal loads. This Rey et al. [8] for dual fuelling with primary reference fuel
and hydrogen. As the piston approaches TDC, the methane-
is demonstrated in Figure 7.
air mixture in the squish volume is subjected to heat and
pressure from the compression as well as heat from the hot
exhaust valves and preignition reactions progress almost to
the point of self ignition. As the flame reaches the end of the
piston bowl and enters the squish volume, the volatile
mixture is consumed almost instantly and causes a sharp
increase in the ROHR. As EGR is added to the mixture the
temperatures are lowered and the preignition reactions in the
end gas progress more slowly. At 20% EGR, the flame first
quenches at the entrance of the squish volume and it is not
until 12°ATDC that a sufficient clearance exists so that the
flame will enter the squish gap. When the EGR rate is
increased to 40%, no increase in the ROHR corresponding to
combustion of the squish volume can be seen. Instead the
mixture in the squish and crevice volumes is oxidized more
slowly as it mixes with the burning and burned gases from
the piston bowl. This slower, cooler combustion is less
efficient than the rapid HCCI-like combustion of the baseline
case and eventually leads to more HC being emitted into the
exhaust but produces much less noise and stress on the
hardware. The combustion efficiency at stoichiometric
Figure 7. Emissions of HC and NOx versus λ for three operation is 99% using no EGR and 98% and 96% using 20%
and 40% EGR respectively. It is important to keep in mind
different EGR rates at 13 bar BMEP
that when EGR is used in a full engine, the unburned HC is
recirculated back into the engine and given a second chance
The NOx emissions from the baseline case follow the known to oxidize; this phenomenon is not present in this data since
trend from lean burn SI engines with a peak in BSNOx EGR from a separate engine is used. This can be expected to
emissions around λ=1.1−1.2. This is the result of a tradeoff reduce HC emissions further when high EGR rates are used.
between the need for surplus oxygen to form NOx and the
cooling effect of diluting the mixture which reduces the NOx PILOT SIZE
formation rate. Moderate rates of EGR can be used with good As previously mentioned, the different pilot sizes result in a
effect to reduce NOx in a lean burn engine throughout the diesel substitution rate of 98% for the baseline case and 80%
lambda range. The use of 20% EGR results in a 75% and 70% respectively for 29mg and 48 mg diesel pilot. The
reduction of BSNOx at λ=1.2 with only a moderate penalty in brake specific emissions of HC and NOx are shown in Figure
BSHC. The lean limit is reduced when using EGR. This is of 9.
less importance since the need for exhaust pressure in excess
of intake pressure to drive EGR eliminates the potential for
positive pumping work from the turbocharger. This removes
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Figure 8. Temperature and rate of heat release versus CA for three different EGR rates at 13 bar BMEP, λ=1

As the diesel pilot is increased the lean limit of the engine is One explanation for the decrease in NOx is the decrease in
increased substantially, this is expected and in line with temperature as the diesel pilot increases in size. For the
previous work on the area. At high λ, the diesel pilot is the baseline case, combustion is essentially finished at
main source of NOx emissions. This is well documented in 14°ATDC. The after oxidation of heavier hydrocarbons and
the literature [2], and supported by the data; at λ > 1.8, there soot particles from the diesel fuel takes additional time and
is a strong correlation between the NOx emissions and the progresses further into the exhaust stroke for the 29 and 48
size of the diesel injection. Between λ=1.2 and λ=1.6, mg case. These combustion characteristics result in a peak
however, the opposite is true, the NOx emissions decrease as temperature that is roughly 100 K and 150 K higher for the
the pilot injection increases in size. In an effort to explain baseline case compared to the 29 mg and the 48 mg case
this, the operating points at λ=1.2 are investigated in further respectively. This explains some of the reduction in NOx. In
detail in Figure 10.
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In step 3, the diesel ignites and flame propagation starts in the

surrounding methane, the local λ is richer than 1.2.

In step 4, the flame propagates through the remainder of the

methane-air mixture where λ is substantially leaner than
global λ.

The aforementioned heterogeneities in the combustion

chamber means that the bulk of the combustion takes place at
local conditions richer or leaner than the global λ, thus
avoiding the peak in NOx formation at λ=1.2. This effect
increases in magnitude when larger pilots are employed and
vice versa. To summarize; the reduction in NOx formation at
low λ and large pilot injections is likely the result of two
phenomena:

• Reduced peak temperature

• Heterogeneity in the combustion chamber, the local mixture
is leaner and richer than the global mixture.
Figure 9. Emissions of HC and NOx versus λ for three
It appears that the diesel pilot is the main source of the NOx
different pilot sizes at 13 bar BMEP
emissions at mixtures leaner than λ≈1.6, while at richer
mixtures the NOx is the result of the deflagration combustion
search of other mechanism relevant to the reduction in NOx, through the methane-air mixture.
clues can be found by recapitulating each step of the DDF
combustion process and reviewing how they are affected by a INLET TEMPERATURE
change in pilot size and diesel substitution rate: Problems with knock and preignitions limited engine
operation to mixtures leaner than λ=1.3 when the inlet
1. A homogenous mixture of air and methane is compressed.
temperature was increased to 60°C. Emission results can be
2. At the end of compression a diesel pilot is injected at high found in Figure 11.
pressure and most, if not all of the injection takes place
during the ignition delay, which means that the diesel For all values of λ, the NOx emissions are higher when a high
vaporizes and forms a diesel-methane-air mixture in the inlet temperature is employed, the reason for this is self
lower portions of the piston bowl prior to ignition. evident since higher inlet temperatures lead to higher peak
temperatures and will not be discussed further. Of greater
3. The diesel vapor ignites in multiple locations around the interest is the large increase in the lean limit achieved with a
piston bowl relatively moderate increase in inlet temperature. Raising the
inlet temperature from 30°C to 60°C allows for stable
4. Flame propagation, initiated at the diesel flame kernels,
operation and moderate HC emissions at λ=2.4, compared to
takes place through the remainder of the methane-air mixture.
a temperature of 30°C, where λ>1.8 results in a substantial
increase in BSHC. This highlights the potential for the DDF
In step 1, an increase in the size of the diesel pilot means that
engine to operate at extremely lean mixtures, given the right
less of the energy will be supplied by methane, which in turn
conditions, with resultant benefits in BSNOx and efficiency.
means that λ in the homogenous methane-air-mixture, is
leaner. When the pilot is increased to 48 mg, λ in the The operating points at λ=1.9 using the baseline settings and
methane-air mixture is actually 1.6, even though the global λ λ=2 using high inlet temperature are selected for further study
is 1.2. in Figure 12.

In step 2, the mixture of diesel vapor, methane and air present

in the piston bowl prior to ignition is richer than the global λ
since the diesel is not evenly distributed throughout the entire
combustion chamber.
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Figure 10. Temperature and rate of heat release versus CA for three different pilot sizes at 13 bar BMEP, λ=1.2

Figure 11. Emissions of HC and NOx versus λ for two different inlet temperatures at 13 bar BMEP
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Figure 12. Temperature and rate of heat release versus CA two different inlet temperatures at 13 bar BMEP, λ=1.9 and λ=2

When the inlet temperature is raised, the temperature in the SUMMARY/CONCLUSIONS

cylinder is higher throughout the combustion and the ROHR
An experimental investigation has been carried out to
displays a peak at approximately 10° ATDC, most likely
characterize and investigate the potential for dual fuel
corresponding to bulk ignition of the fresh charge in the
combustion utilizing all degrees of freedom available in a
squish volume, similar to what was discussed in the section
modern diesel engine. To control the engine and test bed,
about EGR. The results are similar, the rapid combustion
actuate the injectors and facilitate fast and easy
leads to higher combustion efficiency and a reduction in
implementation of control strategies a rapid prototyping
BSHC; in this case the reduction is almost 50%, from 13.5 to
control system has been used, AVL RAPTOR.
8 g/kWh. Raising the inlet temperature is identified as a
relevant tool to increase the combustion efficiency, in
The study achieved the following results:
conjunction with high levels of EGR and stoichiometric
operation it could lead to a very competitive combustion • Advanced combustion phasing can be used to improve
concept. combustion efficiency and extend the lean limit of the DDF
engine. This practice results in a penalty with regards to NOx
emissions and thermal efficiency.
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• Moderate levels of EGR are extremely effective at reducing 7. De Simio, L. Gambino, M., Iannaccone, S., (2007). Low
NOx emissions but impose a penalty with regards to the lean Polluting High Efficient Mixed Fuel Natural Gas Engine for
limit. Transport Application, Urban Transport XIII, Urban
Transport and the Environment in the 21st Century, 493-502.
• High levels of EGR, 40%, can be used to reach
stoichiometric conditions which greatly reduce the cost of the 8. Rey, S. et al., (2010). Condition of SI-CI Operation with
aftertreatment system by enabling the use of a TWC. Using Lean Mixture of Primary Reference Fuel and Hydrogen.
high levels of EGR imposes a penalty on BSHC and International Journal of Automotive Engineering 2.
combustion efficiency.
• The diesel pilot is the main source of NOx emissions at lean
CONTACT INFORMATION
mixtures, λ>1.6. At richer mixtures, NOx is mainly produced FREDRIK KÖNIGSSON, MSc
from the high temperatures which are a result of the fredrik.koenigsson@avl.com
deflagration combustion through the methane-air mixture. www.avl.com

• Reducing the diesel substitution at low λ can reduce the

NOx emissions significantly. DEFINITIONS/ABBREVIATIONS
• Increasing the inlet temperature can extend the limit for lean CNG
operation substantially. Compressed Natural Gas

• Stoichiometric combustion with EGR in conjunction with

GHG
raised inlet temperature is identified as an interesting field
Green House Gas
and holds great potential since it enables the use of an
extremely cost effective aftertreatment system.
DDF
REFERENCES Diesel Dual Fuel

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Environment,” SAE Technical Paper 2011-01-0711, 2011, SI
doi:10.4271/2011-01-0711. Spark Ignited

2. Karim, G., Liu, Z., and Jones, W., “Exhaust Emissions

from Dual Fuel Engines at Light Load,” SAE Technical BMEP
Paper 932822, 1993, doi: 10.4271/932822. Brake Mean Effective Pressure

3. Tunestål, P. (2009). Self-tuning gross heat release

computation for internal combustion engines. Control MBT
Engineering Practice 17, 518-524. Maximum Brake Torque
4. Tomita, E., Kawahara, N., Piao, Z., and Yamaguchi, R.,
“Effects of EGR and Early Injection of Diesel Fuel on CA
Combustion Characteristics and Exhaust Emissions in a Crank Angle
Methane Dual Fuel Engine,” SAE Technical Paper
2002-01-2723, 2002, doi:10.4271/2002-01-2723. CA50
Crank Angle of 50% burned
5. Lin, Z. and Su, W., “A Study On the Determination of the
Amount of Pilot Injection and Rich and Lean Boundaries of
the Pre-Mixed CNG/Air Mixture for a CNG/Diesel Dual-Fuel HC
Engine,” SAE Technical Paper 2003-01-0765, 2003, doi: Hydrocarbons
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Review. Renewable and Sustainable Energy Reviews 13,
1151-1184.
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CO
Carbon Monoxide

BSHC
Brake Specific HC emissions

BSNOx
Brake Specific NOx emissions

EGR
Exhaust Gas Recirculation

AFR
Air to Fuel Ratio

HCCI
Homogenous Charge Compression Ignition

TDC
Top Dead Center

ROHR
Rate Of Heat Release

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